Re: [RFC v3 2/8] vfio/type1: Make per-application (VM) PASID quota tunable

Alex Williamson
2020-01-29T23:56:47Z

On Wed, 29 Jan 2020 04:11:46 -0800
"Liu, Yi L" <yi.l.liu@intel.com> wrote:

> From: Liu Yi L <yi.l.liu@intel.com>
>
> The PASID quota is per-application (VM) according to vfio's PASID
> management rule. For better flexibility, quota shall be user tunable
> . This patch provides a VFIO based user interface for which quota can
> be adjusted. However, quota cannot be adjusted downward below the
> number of outstanding PASIDs.
>
> This patch only makes the per-VM PASID quota tunable. While for the
> way to tune the default PASID quota, it may require a new vfio module
> option or other way. This may be another patchset in future.

If we give an unprivileged user the ability to increase their quota,
why do we even have a quota at all? I figured we were going to have a
module option tunable so its under the control of the system admin.
Thanks,

Alex

>
> Previous discussions:
> https://patchwork.kernel.org/patch/11209429/
>
> Cc: Kevin Tian <kevin.tian@intel.com>
> CC: Jacob Pan <jacob.jun.pan@linux.intel.com>
> Cc: Alex Williamson <alex.williamson@redhat.com>
> Cc: Eric Auger <eric.auger@redhat.com>
> Cc: Jean-Philippe Brucker <jean-philippe.brucker@arm.com>
> Signed-off-by: Liu Yi L <yi.l.liu@intel.com>
> ---
> drivers/vfio/vfio_iommu_type1.c | 33 +++++++++++++++++++++++++++++++++
> include/uapi/linux/vfio.h | 22 ++++++++++++++++++++++
> 2 files changed, 55 insertions(+)
>
> diff --git a/drivers/vfio/vfio_iommu_type1.c b/drivers/vfio/vfio_iommu_type1.c
> index e836d04..1cf75f5 100644
> --- a/drivers/vfio/vfio_iommu_type1.c
> +++ b/drivers/vfio/vfio_iommu_type1.c
> @@ -2243,6 +2243,27 @@ static int vfio_iommu_type1_pasid_free(struct vfio_iommu *iommu,
> return ret;
> }
>
> +static int vfio_iommu_type1_set_pasid_quota(struct vfio_iommu *iommu,
> + u32 quota)
> +{
> + struct vfio_mm *vmm = iommu->vmm;
> + int ret = 0;
> +
> + mutex_lock(&iommu->lock);
> + mutex_lock(&vmm->pasid_lock);
> + if (vmm->pasid_count > quota) {
> + ret = -EINVAL;
> + goto out_unlock;
> + }
> + vmm->pasid_quota = quota;
> + ret = quota;
> +
> +out_unlock:
> + mutex_unlock(&vmm->pasid_lock);
> + mutex_unlock(&iommu->lock);
> + return ret;
> +}
> +
> static long vfio_iommu_type1_ioctl(void *iommu_data,
> unsigned int cmd, unsigned long arg)
> {
> @@ -2389,6 +2410,18 @@ static long vfio_iommu_type1_ioctl(void *iommu_data,
> default:
> return -EINVAL;
> }
> + } else if (cmd == VFIO_IOMMU_SET_PASID_QUOTA) {
> + struct vfio_iommu_type1_pasid_quota quota;
> +
> + minsz = offsetofend(struct vfio_iommu_type1_pasid_quota,
> + quota);
> +
> + if (copy_from_user(&quota, (void __user *)arg, minsz))
> + return -EFAULT;
> +
> + if (quota.argsz < minsz)
> + return -EINVAL;
> + return vfio_iommu_type1_set_pasid_quota(iommu, quota.quota);
> }
>
> return -ENOTTY;
> diff --git a/include/uapi/linux/vfio.h b/include/uapi/linux/vfio.h
> index 298ac80..d4bf415 100644
> --- a/include/uapi/linux/vfio.h
> +++ b/include/uapi/linux/vfio.h
> @@ -835,6 +835,28 @@ struct vfio_iommu_type1_pasid_request {
> */
> #define VFIO_IOMMU_PASID_REQUEST _IO(VFIO_TYPE, VFIO_BASE + 22)
>
> +/**
> + * @quota: the new pasid quota which a userspace application (e.g. VM)
> + * is configured.
> + */
> +struct vfio_iommu_type1_pasid_quota {
> + __u32 argsz;
> + __u32 flags;
> + __u32 quota;
> +};
> +
> +/**
> + * VFIO_IOMMU_SET_PASID_QUOTA - _IOW(VFIO_TYPE, VFIO_BASE + 23,
> + * struct vfio_iommu_type1_pasid_quota)
> + *
> + * Availability of this feature depends on PASID support in the device,
> + * its bus, the underlying IOMMU and the CPU architecture. In VFIO, it
> + * is available after VFIO_SET_IOMMU.
> + *
> + * returns: latest quota on success, -errno on failure.
> + */
> +#define VFIO_IOMMU_SET_PASID_QUOTA _IO(VFIO_TYPE, VFIO_BASE + 23)
> +
> /* -------- Additional API for SPAPR TCE (Server POWERPC) IOMMU -------- */
>
> /*